Generally, fan motors used in electronic appliances such as computers and household appliances such as refrigerators are largely adopted as outer rotor type fan motors that can be made compact in the radial direction and the axial direction in consideration of their installation space.
In the conventional outer rotor type fan motor, since the stator adopts the core type, the height of the motor cannot be reduced. Also, since the diameter of the bearing provided at the center of the stator and supporting the rotating shaft is limited, there is a problem that sufficient oil cannot be contained therein.
Meanwhile, an axial flow fan using a coreless flat brushless motor in anticipation of ultra-lightness, ultra small size, and long life is proposed.
The axial flow fan is constituted by an axial type motor in which the field magnet of the rotary fan and the armature coil are in a face-to-face fashion, but since the structure in which an air core type armature coil is disposed in a coil installation portion is adopted, there is a problem that the height of the stator is not reduced any more.
In addition, the stator of the fan motor is constituted by stacking a stator yoke and a single-phase armature coil on top of a PCB, and a pair of ball bearings are built in a bearing holder at the center of the PCB to support the rotating shaft. However, there is a problem that the stator cannot be thinned.
Meanwhile, a small-sized fan motor is reduced in size and a single-phase motor having a single coil is used in consideration of cost burden. In this case, the single coil is wound in a quadrangular or triangular coreless/bobbinless type and mounted on a PCB as disclosed in Korean Registered Utility Model publication No. 20-0296035 (Patent Document 1).
BLDC motors are synchronous motors with fast dynamic response, low rotor inertia and easy speed control.
When a brushless direct current (BLDC) motor is used as the single-phase motor, a Hall sensor for rotor position detection is required to detect the N-pole and S-pole magnetic poles of the rotor to generate a switching signal of the driving current to the stator coil and the Hall sensor is expensive. Therefore, it is preferable to use a driving circuit using only one Hall sensor.
In this case, in the case that a single Hall sensor is used, the magnetic pole of the Hall sensor is not detected when the Hall sensor is located at the interface of the rotor magnetic pole, and thus the current cannot be supplied to the stator coil. Therefore, there is a dead point at which the starting cannot be performed.
In such a single Hall sensor system, there is a method in which auxiliary magnets are used so that the Hall sensor deviates from a magnetic pole interface (that is, a neutral point) of a rotor by using a magnet for fixation to the stator as a self-starting scheme so as to avoid the dead point, and there is also a method of using a dead point prevention yoke of a special shape as in Patent Document 1.
In the case of using a Hall sensor for rotor position detection for generating a switching signal of the driving current for the stator coil, the cost increase factor occurs since it is necessary to use an expensive Hall sensor and to mount the additional components for the self-starting. Therefore, there is a demand for a method of generating a rotor position signal while minimizing the cost increase factor without using the Hall sensor.
In addition, various sensorless motor driving methods have been proposed for detecting rotor position signals without using a Hall sensor. Among the various sensorless motor driving methods, it is possible to employ a double winding method in which a main coil is wound first and an auxiliary coil for detecting the rotor position is wound once again and extended from each coil to be connected to the drive circuit. However, such a double winding method has a disadvantage that it is difficult to use it because of its complicated structure and complicated winding.
Furthermore, in the case of a small fan, the coil is composed of fine wires in a general coil winding method in which a stator coil is wound on a bobbin, a stator coil is wound in a bobbinless type, or a stator coil is wound on a core. Therefore, when the thickness of the coil is constant in the start line and the end line, there is a problem that the start line and the end line may be broken due to careless handling or vibration during soldering, or the manual soldering process may be defective.
Meanwhile, when wireless power transmission (particularly, rapid charging) is performed to the terminal, the wireless charger generates a lot of heat in the transmission coil and the electronic component, and the charging efficiency is lowered. Accordingly, a cooling fan for preventing a temperature rise in the wireless charger by an air cooling method is required. A fan motor that is slimmer and smaller than the conventional fan motor is required for such a cooling fan.